Tesco Hudl2 battery problems and teardown - Part2

Following on from my previous post (Tesco Hudl2 battery problems and teardown) I ordered a replacement Li-Ion battery (from eBay) to compare and test if this was the problem.

The battery was identical to the original one I had (Apart from the screenprinting wasn't quite a clear, so I'm not sure if it was genuine or a chinese copy. Doesn't really matter!), and so the first thing I did was tested the voltages I was getting on the pins.
Again on the black and red wires I was getting around 3.9v which looked good. I then tested the yellow and green wires. As you may remember these were the two I was most interested in as I think they were 'sense' wires to the Hudl2 to perhaps control if it should power on, check for 'safe' state of the battery, etc.
These did the same as the original battery, same low voltage output and same floating values, however after a bit of thought I tried the test but against the red (positive) wires, and lo and behold I got values! I got the same 3.9v on both of these wires. Comparing to the old battery, that did the same, so now I know, both batteries are giving the same output.
Therefore I wasn't very hopeful at this making the Hudl2 work.
Connecting it up, and sure enough the Hudl2 wouldn't power on. Connecting the charger up it again didn't light the charge light. No luck.

I then took the main board out of the Hudl2 to look for any other signs of problems, couldn't find anything, many many probe pins are on the board underneath marked power, signal, etc, and probing almost all of these showed voltage and signal so the board was getting power, etc, and all looked OK, so it appears to be something a lot more fundamentally wrong with the board now.

My suspicion is that when the fault PSU/wire started shorting out the usb input, there wasn't enough protection on the board and it damaged some key components (Not just in the charge circuit/components) and effectively bricked the unit.

Tesco Hudl2 battery problems and teardown

The Hudl2 is an excellently priced android-based tablet sold by Tesco in the UK for a while. Unfortunately they have now discontinued the range and so no more will be produced. Their price-point of under £100 and has an 8.1" screen, full HD, stereo speakers, quad-core 1.8Ghz processor, 2Gb RAM, 16Gb storage built-in and a 5 megapixel rear camera and 1.2 megapixel front-facing camera. So a pretty decent spec for the money.
My youngest had one and it's done well, lasted around 2 years of abuse, mainly around the charge socket as usual it's micro-usb and this is the weak point, the cables were abused quite badly and over time gave up, so swapping cables quite often solved it. That was until the last time, when the cable seemed to have shorted, so the tablet was left for a few weeks totally flat.
Plugging it in to charge wouldn't give the red charging light, which worried me as normally charge lights are hard-wired to the voltage input, so it not coming on was a bad sign, was the usb port damaged or worse.

What makes it more complicated is the hudl2 comes with a USB charger, but with non-standard specs, it's the usual 5v output but it's 2.0A which is a lot higher than normal (usb port is 0.5A), so that would suggest the hudl2 uses fast/high-powered charge. I therefore wasn't sure what the cable needed to be (We'd thrown out the damaged cable, a stupid move in hindsight!). Luckily the charger itself was OK and charging other USB devices fine.

So I suspected the hardware, popping the cover off is easy, just a flat screwdriver gently prising around the outside of the case at the seam will take the back cover off, just pop it open and it comes into two neat halves (no wires to worry about popping out, etc, the rear cover is purely a cover).

There in the middle you can see the 'battery pack'. This consists of two 3.8v li-ion batteries in parallel which I assume is to provide longer life/capacity. The connector is curious, it's 10 wires, 4 red, 4 black, one yellow and one green. All the red wires are tied together (so I suspect just to carry higher current on small wires) as are all the black wires. The yellow and green are interesting.
Upon initial opening, the red and black wires were giving 0v output. This made me think the 'battery pack' had li-ion protection circuit in there and had gone into full discharge protection (i.e. shutting the batteries down). So the first trick was to get them to charge. Plugging the USB power lead in initially didn't show any voltage on these wires either, which really confused me, as I'd assume the tablet would provide power to try and charge the batteries and rely on the charge circuitry to protect it.
In hindsight, I suspect this isn't the case, and the tablet does have sense on it (through the yellow and green wires I think) and so didn't start charging.

I then pulled apart the battery pack (very carefully. Li-ion are very unstable batteries, any damage could cause a cascade accident so please read up on them and do this with caution, know what you're playing with!) and found the control circuit. This was also when I found that the 'battery pack' was two li-ion packs joined together at the top with the control circuitry.
Testing the cell themselves (the metal tabs at the top of the cells) I got a low voltage (around 3.0v) which I'd guess was too low for the circuit to allow output/charge, so it was 'dead'. Reading around, there are ways to revive this circuit, unfortunately I didn't really document how I recovered the battery but it was a combination of keeping the charge on it and probing the sense circuits (My suspicion is my meter combined with voltage applied caused the charge circuit to 'see' a voltage which kicked things back off). I then saw 3.7v on the red and black wires from the Hudl2 cables, which was a good start. Watching it over a minute or so I saw the voltage slowly going up, by 0.01v every few seconds, so it got to 3.9v and hovered for a while. This looked hopeful.
Meanwhile I took it off charge a few times to test the Hudl2 power supply, the adapter gave out 5v as expected, and it had the middle two data pins shorted out, which is a common way of signalling to devices that it was a 'fast/high capacity' charger, so that's why other chargers didn't work right, they did slow/low charging rates.
Over about 30 minutes the voltage went up and up to around 4.0v which looked a good charge voltage for the cells, and it stayed around there, the charger got quite warm (I couldn't check current unfortunately) but I guessed this meant it was charging at a decent rate.
Over a few hours the voltage stayed around 4/4.1v and when removing the charger, I saw the voltage drop to the correct 3.8v supplied on the black and red wires to the Hudl2. However, the charge light would still not come on and the tablet wouldn't power on.
I was using the 'recovery' way of turning it on, that is holding the volume up and power in for 15 seconds, then just power for 15 seconds. This is supposed to recover it should it stop charging. However this wouldn't work. I've tried many combination of power and volume buttons without success now. None will show either the charge light or the power coming on to the tablet (Normally even when low on battery plugging the charge cable in would light the screen up and show a charging battery animation, this didn't trigger either).
So I'm back to suspecting the 'sense' circuitry either in the battery (unlikely as the batteries seemed happy now) or in the Hudl2 itself (most likely now I think). So I turned my attention to the strange additional two wires. The Yellow and Green that came from the battery into the Hudl2 motherboard.
When testing these wires, the yellow shows a constant 0.5v (when tested to black/ground) and the green showed a jumping voltage, my meter only showed around 0.5v for about a second, then 0 then back up again, approx every second changing. This is confusing, I'm unsure what both of these values should be, so cannot determine if these are giving the right output to the Hudl2 to tell it 'all is well'.

This is where I'm up to, the tablet won't power on or show it's charging, I think it's to do with these two sense cables, but not knowing their purpose or correct values cannot 'trick' it into booting or charging, which I suspect will kick a chain reaction and get it back to life.
I've ordered a replacement Li-Ion battery pack for it (Around £10 from eBay) as my suspicion is that if the pack is still damaged/faulty, then these sense wires may be causing the problem. When the new pack arrives the first thing I'll be doing is testing these two leads and see what voltage they give out and what sequence they do, as that may unlock the key to why the unit won't power back up.

As always, I'd appreciate your feedback and comments, if you've had similar problems and solved them please do post back to me, or if you know what the mystery Yellow and Green wires are for let me know in the comments!

Arduino shed/outdoor monitor, batteries and solar panels

A brief update, I put in place my shed/outdoor monitoring system last weekend, installed the solar panel and monitors, and have so far had to change the batteries already, so at the moment it looks like they are only lasting 3-4 days maximum.

Upon investigating my 9v solar panel is giving out 2-3 volts, which is pretty useless. I'm trying to charge my 4 AA batteries (6 volts).

So my next plan of action is to take the solar panel back down and work out why it's only producing this very low voltage, I'm now wondering if the connections on the rear split the panel into two and I'm only connecting to one half (even so doubling 3 volts isn't near the 9v I was expecting), so a bit more investigation is needed.

(Yes I removed the plastic film cover! But it is inside a plastic box for protection, but even so I'd not expect the voltage drop to be that dramatic)

Graphs were being produced before the power failure though as you can see below:

(note the flat line towards the end is where the batteries died and I'd not written a failsafe into my graphing to 0/ignore results)

Arduino ESP8266 1-wire Dallas temperature, soil, rain, moisture, solar power unit

Arduino Uno outdoor sensors project. Here is the first posting for my Arduino UNO outdoor monitoring unit. The idea for this is to act as a small weather station, and also to feedback on the condition of the garden. So this is my second version of my earlier garden controller (several years ago).
I bought a bunch of sensors recently, which included:

• 1-wire Dallas temperature sensor DS18B20
• Rain sensor module with LM393
• Light dependant resistor LDR5528 (+10k resistor)
• Soil moisture sensor with LM393
• ESP8266 wifi module
• 9v Solar panel + 1N4007 diode
• Water float sensors (x2)

The goal is to setup a stand-alone Arduino that will connect to my wifi (signal may be an interesting problem, we'll come to that) and then feed back a lot of environmental information to my server, that I can then graph/log and alert depending on the inputs.

ESP8266:

First job was to get the ESP8266 wifi module working. This was a new item to me, but it's principle was simple, it was a stand-alone wifi module that you could communicate using 2-wires serial (TX and RX), so you could open a serial session, connect to your wifi AP using WPA2, WEP, etc, and then set it to send data in an HTTP GET session. The simple commands made this an excellent add-on for me to include in my project, and the price is excellent (Around £3).

Connecting it up, you need power (3.3v), also you need to pull CH_PD to positive, which I did through a 10k resistor. So my wiring diagram worked out as:

(Credit to enio in arduino forums for image)

I connect VCC, GND, CH_PD for power. then TX and RX to the Arduino. To test the connectivity I used my Arduino UNO, loaded a blank sketch and connect RX to data_rx and TX to data-tx (pins 0 and 1 digital), that let me type into the serial console and it was passed straight to the ESP8266. Various AT command sets are available all over the internet, so a few tests I did:

AT

AT+CWLAP

(Full list on wikipedia http://wiki.iteadstudio.com/ESP8266_Serial_WIFI_Module#AT_Commands)

After receiving valid replies I knew the unit was operating correctly, and making a quick sketch to connect to my WIFI using softserial started working (using softserial allowed me to use alternative digital pins for talking to the ESP8266 whilst still having my serial console to monitor and upload sketches).

After some trial and error, I found this wifi module dropped out or didn't respond to commands. Upon checking various forums and information, I found this was probably due to the current this was pulling. Originally I was powering it via the 3.3v output on the Arduino, however this couldn't provide enough power, especially when I added all my other sensors, etc and I started to get issues with no reply to the AT commands. Therefore I decided I needed to power this separately. The solution (since I would be powering this from a bank of AA batteries) was to use a LM2596 DC-DC step-down power supply (also known as a buck converter).

I set this up on my multimeter and set it to produce 3.3v so this would supply the ESP8266 directly. (I'll have to see over time how inefficient this method would be, as I know it'll be wasting energy from the battery packs)

1-wire temperature sensor DS18B20

I've used these temperature sensors many times before, I have one in each of the Raspberry PI's around the house and have created a basic temperature 'network' within the house to monitor room temperatures in previous blog posts. I'm using the same sensor again, so as before simply connecting the 3 pins up and including the "OneWire.h and DallasTemperature.h" libraries into my sketch and it was up and running. PIN connections for the DS18B20 are as follows:

  

So in my setup (You can't quite see this in the picture unfortunately as it's wrapped in black tape) I have connected GND to ground, VDD to +5v, DQ to a digital pin, and then via a 4k7 resistor DQ is also connected to 5v.

Soil moisture sensor with LM393

The soil moisture sensor is a regular two pin/probe style that you stick in the ground, and then measure the resistance between pins. The unit I bought came with a basic LM393 control circuit shown below:

 

The pin connections are simple, on the left you connect the soil measuring probe, the right are 4 connections, top and bottom are +VE (3.3v) and GND, then you have an analogue out or digital out. The digital out (high or low) is controlled using the variable resistor on the board, so you can set the threshold. I opted for analogue so connecting to the analogue inputs and then read the values shown. Read this as a typical integer from the digital input.

Rain sensor with LM393

This is the same as the soil moisture sensor and came with the LM393 sensor as above.

9v solar panel

To power my arduino I decided to go with a battery pack and use a solar panel to top the batteries up. I purchased a battery pack, the model I chose had 6xAA batteries so produced approx 9v. This created several problems. Firstly the cheap solar panel I bought only produced 220ma 2 watts at 9v, so even at full sunlight it was producing the same voltage as the batteries, therefore this would not charge them (generally you need a higher voltage to charge) and at low current.

Therefore I decided to modify my battery pack to exclude 2 AA batteries, taking the voltage down to 6v which would be more suitable for the solar panel to charge them, and also will reduce the amount of power lost through the heat dissipation on the Arduino Uno.

(NOTE, I'm not an expert on batteries and power, so please do correct me if I make some glaring errors here!)

These are the solar panels I'm using (A chinese import) and currently with their protective plastic film over them. I'm planning on fitting these into a plastic container, to keep them protected from the elements. Although this will reduce their output slightly it will protect them over time.

I should also mention that I have connected in a 1N4007 1A 400v rectifier diode to ensure no power from the batteries are lost back into the solar panels during darkness, etc.

Below is the power pack that I've put in my two dummy batteries to reduce the voltage/number of cells:

Testing the Arduino Uno and the LM2596 powering all the devices the pack was providing enough power. I'll monitor this for amount of current consumed, etc, later in the testing/implementation.

Light Dependant Resistor LDR5528

This was a simple off the shelf LDR that I connected up to the Arduino analogue input ports with a 10k resistor in parallel (to the 5v feed). I then read this during the normal sampling periods.

CODE

The code I've used is a combination of various of my older projects put together with some libraries to control the various input sensors. The libraries I've used are as follows:

#include <LowPower.h> - This is to be used to help reduce idling power consumption

#include <stdlib.h> - for dtoi and related functions

#include <SoftwareSerial.h> - for communication to the ESP8266

#include <OneWire.h> - for the 1-wire temperature communication protocol

#include <DallasTemperature.h> - 1-wire temperature

I set a few definitions near the top of the code (for SSID, WPA2 password and the url to GET when sending data).

Setup involves setting the various input and output pins to their relevant values and initialise the softwareserial.

The main code loop is fairly straight forward, I read each of the sensors in turn, display the output to the serial monitor and then use the ESP8266 to send the data to my webserver.

The code is available in full on my github page, so feel free to take a look, and if you can spot any improvements please commit them as I'd like to get some feedback and improvements on my code:

https://github.com/andyb2000/outdoor_sensors

(NOTE: There are a few extras I've missed off here, I'll post further blog entries with tweaks and changes as I make them and when I implement the final system)

UPSs tinkering

Doing a bit of tinkering with UPSs (Uninterruptible Power Supplies) for the FM station I help out at, and been discovering some interesting fact and details that I'm making note of, again more for my benefit that others probably!

Firstly, the problem. Several old UPS units well past their prime have been in use to smooth the power out and keep the equipment going for all those little blips in power, this is to provide power to an FM transmitter, audio processor and RDS encoder. All together they don't draw a huge amount of power (approx 130 watts), but I need them protected against surges and other nasties, also the power in our particular location isn't very good, drops out often and suffers from surges, brownouts and all sorts, so protecting this sensitive and expensive equipment is a must.

I've used a variety of APC, Belkin and no-name UPSs for this job, mainly ones I've salvaged and either got working enough by cycle charging them or pure luck, and they hold up for at least a few minutes in a power failure which smoothes out most of the dips we get. Now I had a chance to properly replace a couple, the first was my old ALC Smart-UPS sc420 which is a reasonably new model (4 years approx), and I didn't use as it was alarming about battery failure. So looking to purchase a new battery, hit the APC website and they wanted me to trade the whole UPS in for a replacement. This seems excessive, it only needs a new battery. So, all of these units are able to be replaced, taking the battery out, it's a regular sealed lead-acid (or gel, I'm not sure) battery. Looking it up, APC call it the RBC2 which is a single unit 12v battery. You can get replacements relatively cheap, in this case around the £25 mark including delivery, so that was a no-brainer, order that, swap the battery and off we go. Went well, and now using it's monitoring on my linux server (apcupsd) it's currently showing it's at 55% load capacity, battery at 100% and approx 16 minutes of run-time available. Excellent, so that solves the immediate problem.

I therefore now have a 'spare' UPS to tinker with, and this one has a bit more power behind it. This one is the APC smart-ups 1500, and after looking it up this can deal with 980 watts at max, so this is a pretty decent size unit (It's also quite heavy!), so again pulling it apart to see what batteries it has, and this one has two joined together. The pic below shows what configuration it has:

These are considerable larger batteries than the RBC2 units, and you can see there are two joined together. On the right terminals (the blue block) is a large fuse joining the terminals together, and on the left you see the cables that are connected into the UPS itself (the yellow marks are the adhesive that had covers over all the exciting bits). Taking it all apart, I'm expecting two 12v batteries again, so joining them in series like this would give a 24v pack. Each battery was registering around 2v on their own, and so seem pretty dead to me (This ups is probably more like 10 years old, and in my use it died probably 2yrs ago and has been left unplugged ever since, so I suspect sulphurisation has occurred and completely ruined them), so onto the next thing, identifying so I can replace. This isn't easy.

APC batteries are completely generic, no markings, or anything. I suspect they either burn, scrub or simply cover all markings showing voltage, current, etc, which makes it harder. Luckily most websites have direct lookups for these batteries, just put in the ups product and it'll tell you what size, etc. So that looks like the next plan, to order a couple, wire them up and get this UPS back on the road!